Clinical, genetic, and functional characterization of the glycine receptor β-subunit A455P variant in a family affected by hyperekplexia syndrome

Hyperekplexia is a rare neurological disorder characterized by exaggerated startle responses affecting newborns with the hallmark characteristics of hypertonia, apnea, and noise or touch-induced nonepileptic seizures. The genetic causes of the disease can vary, and several associated genes and mutations have been reported to affect glycine receptors (GlyRs); however, the mechanistic links between GlyRs and hyperekplexia are not yet understood. Here, we describe a patient with hyperekplexia from a consanguineous family. Extensive genetic screening using exome sequencing coupled with autozygome analysis and iterative filtering supplemented by in silico prediction identified that the patient carries the homozygous missense mutation A455P in GLRB, which encodes the GlyR β-subunit. To unravel the physiological and molecular effects of A455P on GlyRs, we used electrophysiology in a heterologous system as well as immunocytochemistry, confocal microscopy, and cellular biochemistry. We found a reduction in glycine-evoked currents in N2A cells expressing the mutation compared to WT cells. Western blot analysis also revealed a reduced amount of GlyR β protein both in cell lysates and isolated membrane fractions. In line with the above observations, coimmunoprecipitation assays suggested that the GlyR α1-subunit retained coassembly with βA455P to form membrane-bound heteromeric receptors. Finally, structural modeling showed that the A455P mutation affected the interaction between the GlyR β-subunit transmembrane domain 4 and the other helices of the subunit. Taken together, our study identifies and validates a novel loss-of-function mutation in GlyRs whose pathogenicity is likely to cause hyperekplexia in the affected individual.

A-type K+ channels impede supralinear summation of clustered glutamatergic inputs in layer 3 neocortical pyramidal neurons

A-type K⁺ channels restrain the spread of incoming signals in tufted and apical dendrites of pyramidal neurons resulting in strong compartmentalization. However, the exact subunit composition and functional significance of K⁺ channels expressed in small diameter proximal dendrites remain poorly understood. We focus on A-type K⁺ channels expressed in basal and oblique dendrites of cortical layer 3 pyramidal neurons, in ex vivo brain slices from young adult mice. Blocking putative Kv4 subunits with phrixotoxin-2 enhances depolarizing potentials elicited by uncaging RuBi-glutamate at single dendritic spines. A concentration of 4-aminopyridine reported to block Kv1 has no effect on such responses. 4-aminopyridine and phrixotoxin-2 increase supralinear summation of glutamatergic potentials evoked by synchronous activation of clustered spines. The effect of 4-aminopyridine on glutamate responses is simulated in a computational model where the dendritic A-type conductance is distributed homogeneously or in a linear density gradient. Thus, putative Kv4-containing channels depress excitatory inputs at single synapses. The additional recruitment of Kv1 subunits might require the synchronous activation of multiple inputs to regulate the gain of signal integration.

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We focus on A-type K+ channels expressed in oblique and basal dendrites.

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Putative Kv4 subunits depress excitatory signals generated by single spine excitation.

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Kv4 and Kv1 regulate supralinear signal integration at clustered dendritic spines.

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A computational model simulates Kv-mediated modulation of dendritic integration.

[PCSK-9 inhibitors, effects on LDL-C and future implications: What you should know]

The discovery of proprotein convertase subtilisin/kexin type 9 (PCSK9) in 2003 in families with familial hypercholesterolemia (HF) later generated the development of pharmacological strategies in order to inhibit this protein. Twelve years after this discovery, the first two biological compounds (monoclonal antibodies) were approved, which have been shown to substantially decrease LDL-C and other lipid subfractions. The objective of the present article is to review the history of the discovery of PCSK9, its physiology and pathophysiology and subsequent pharmacological development. The objectives and goals reached to date and the pending questions regarding the efficacy and safety of its clinical use are presented.

Mutations in SLC12A5 in epilepsy of infancy with migrating focal seizures

The potassium-chloride co-transporter KCC2, encoded by SLC12A5, plays a fundamental role in fast synaptic inhibition by maintaining a hyperpolarizing gradient for chloride ions. KCC2 dysfunction has been implicated in human epilepsy, but to date, no monogenic KCC2-related epilepsy disorders have been described. Here we show recessive loss-of-function SLC12A5 mutations in patients with a severe infantile-onset pharmacoresistant epilepsy syndrome, epilepsy of infancy with migrating focal seizures (EIMFS). Decreased KCC2 surface expression, reduced protein glycosylation and impaired chloride extrusion contribute to loss of KCC2 activity, thereby impairing normal synaptic inhibition and promoting neuronal excitability in this early-onset epileptic encephalopathy.

Endogenous zinc depresses GABAergic transmission via T-type Ca(2+) channels and broadens the time window for integration of glutamatergic inputs in dentate granule cells

Abstract Zinc actions on synaptic transmission span the modulation of neurotransmitter receptors, transporters, activation of intracellular cascades and alterations in gene expression. Whether and how zinc affects inhibitory synaptic signalling in the dentate gyrus remains largely unexplored. We found that mono- and di-synaptic GABAergic inputs onto dentate granule cells were reversibly depressed by exogenous zinc application and enhanced by zinc chelation. Blocking T-type Ca²⁺ channels prevented the effect of zinc chelation. When recording from dentate fast-spiking interneurones, zinc chelation facilitated T-type Ca²⁺ currents, increased action potential half-width and decreased spike threshold. It also increased the offset of the input–output relation in a manner consistent with enhanced excitability. In granule cells, chelation of zinc reduced the time window for the integration of glutamatergic inputs originating from perforant path synapses, resulting in reduced spike transfer. Thus, zinc-mediated modulation of dentate interneurone excitability and GABA release regulates information flow to local targets and hippocampal networks.

Ionotropic receptors at hippocampal mossy fibers: roles in axonal excitability, synaptic transmission, and plasticity

Dentate granule cells process information from the enthorinal cortex en route to the hippocampus proper. These neurons have a very negative resting membrane potential and are relatively silent in the slice preparation. They are also subject to strong feed-forward inhibition. Their unmyelinated axon or mossy fiber ramifies extensively in the hilus and projects to stratum lucidum where it makes giant en-passant boutons with CA3 pyramidal neurons. There is compelling evidence that mossy fiber boutons express presynaptic GABA_A receptors, which are commonly found in granule cell dendrites. There is also suggestive evidence for the presence of other ionotropic receptors, including glycine, NMDA, and kainate receptors, in mossy fiber boutons. These presynaptic receptors have been proposed to lead to mossy fiber membrane depolarization. How this phenomenon alters the excitability of synaptic boutons, the shape of presynaptic action potentials, Ca²⁺ influx and neurotransmitter release has remained elusive, but high-resolution live imaging of individual varicosities and direct patch-clamp recordings have begun to shed light on these phenomena. Presynaptic GABA_A and kainate receptors have also been reported to facilitate the induction of long-term potentiation at mossy fiber—CA3 synapses. Although mossy fibers are highly specialized, some of the principles emerging at this connection may apply elsewhere in the CNS.

[Use of GnRH antagonists (cetrorelix) in assisted reproduction: first report in Mexican literature]

The use of GnRH antagonists in assisted reproduction techniques (ARTs) has been shown to be effective in blocking the luteinizing hormone (LH), without a repercussion on ovaric response. The present study reports the use of a GnRH antagonist (cetrorelix) 0.25 mg/d s.c. in patients stimulated with recombinant FSH (rFSH) for IVF/ICSI. 44 patients with mean age of 33.3 years were included in this study, four patients were receptors for oocyte donation program and another patients was receptor for frozen embryos. Controlled ovarian stimulation was carried out with rFSH, starting on day 3 of menstrual cycle. The total mean dose used was 3.570 +/- 1.102 UI for each patient. The LH serum concentrations were monitored during ovaric stimulation, in two patients a premature LH surge (> 10 UI/L) was detected. The oocytes were collected 36 hours after hCG administration, the mean preovulatory oestradiol was 4.006 +/- 2.418 pg/mL. The mean total oocytes retrieved was 10.8 +/- 7.4 per patient, the fertilization rate was 58.3%, in only three patients fertilization was failed. No difference was observed in oocyte retrieval, fertilization rate, implantation rate between both groups (GnRH antagonists versus GnRH agonists). The embryo transfer was realized on day 3, and only two patients was on blastocyst stage. In 17 of 41 patients with successful transfer, pregnancy was achieved in the group with antagonists, and 8 of 20 patients in the group with agonists. In conclusion Cetrorelix prevents adequately premature LH surges and allows an effective ovaric response in controlled stimulation in IVF cycles, except in patients in oocyte donation programs who require higher cetrorelix doses.

Deep venous thrombosis in the trauma patient

The incidence of deep venous thrombosis (DVT) in the trauma population and those risk factors which affect its development remain an enigma. We prospectively studied 100 trauma patients admitted to a Level I trauma center with duplex scans throughout their hospitalization. Fifteen patients (15%) developed DVT. The remaining 85 patients (85%) had no evidence of DVT during their hospitalization. The two groups were similar in sex ratio, Glasgow coma scale, trauma score, and type of injury. Fourteen patients (93%) with DVT had been given prophylactic treatment with 5,000 units of Heparin subcutaneously q12h, and 36 patients (42%) without DVT were similarly treated. The data in this study describe the incidence of DVT (15%) in the trauma population and those patients at most risk for its development. Patients admitted with high Injury Severity Scores and extremity injuries are at most risk for development of DVT.

Heparin, deep venous thrombosis, and trauma patients

One hundred consecutive patients with multiple trauma, who were admitted to a level I trauma center with an injury severity score of 10 or greater, were studied prospectively. A duplex scan was used to evaluate each patient initially and at set intervals during the hospitalization for the presence of deep vein thrombosis (DVT). The prophylactic regimen for DVT in this study was 5,000 U of subcutaneous heparin every 12 hours. This was used in 50 patients at the discretion of the attending physician, while the remaining 50 patients received no DVT prophylaxis. Fourteen of 50 patients (28%) who were receiving heparin developed DVT, while only 1 patient (2%) of the 50 who did not receive heparin developed DVT. The use of heparin did not provide any significant protection in the susceptible trauma patient. It is believed that those patients with minimal lower extremity injuries, lower injury severity scores, and a shorter period of immobilization do not require any form of DVT prophylaxis. However, those patients at increased risk for DVT are better served with either increased doses of heparin or alternative forms of DVT prophylaxis.

Effects of ischemia and hemoglobin on vascular function in isolated rabbit aortas

The vascular endothelium is important in the modulation of vascular tone via production of endothelium-derived relaxing and contracting factors. The abdominal aortas of five groups of rabbits were subjected to varying lengths of ischemia (0, 1, 2, 3, or 4 hours), removed, sectioned into transverse rings, and placed in tissue baths containing Krebs' buffer at 37 degrees C and aerated with 95% O2/5% CO2. After equilibration the rings were tested for endothelium-dependent vasodilation with methacholine and nonendothelium-dependent vasodilation with nitroprusside. Endothelium-dependent relaxation as elicited by methacholine was impaired at 3 and 4 hours of ischemia but was not significantly different at 1 and 2 hours as compared to control, whereas endothelium-independent vasodilation remained normal throughout the different periods of ischemia. The addition of 1 x 10(-6) mol/L rabbit hemoglobin reduced the time needed to demonstrate significant impairment of endothelial function to 2 hours. Endothelium-independent vasodilation was not affected by hemoglobin. We conclude that hemoglobin exacerbates ischemia vascular dysfunction in the rabbit aorta.